Magnetron



Feb. 9, 1954 E. D. MGARTHUR MAGNETRON Filed April 3, 1952 Fig.6.

Inventor: Elmer D. McArthur,

His Attorney.

Patented Feb. 9, 1954 MAGNETRON Elmer D. McArthur, Schenectady, N. Y.,assignor to General Electric Company, a corporation of New YorkApplication April 3, 1952, Serial No. 280,245

6 Claims. 1

My invention relates to electric discharge devices of the magnetrontype.

Numerous magnetron constructions employing an array of anode segmentsabout a centrally located cathode have been employed. as high frequencyoscillation generators, the anode segments being interconnected in ananode block or by external circuits to provide a resonant outputcircuit. One of the problems arising in the design and operation of suchdevices is caused by the return of high velocity electrons from themagnetron space charge to the cathode. Largely contributing to thisundesired effect are the outof-phase electrons which do not do usefulwork in exciting the resonant output circuits associated with themagnetron anode, and it is accordingly desirable to remove theseelectrons from the interaction space between the cathode and anodesegments to prevent overheating of the cathode.

It is an object of my invention to provide a magnetron discharge devicein which cathode backheating is reduced.

It is another object of my invention to provide a magnetron anode gapconfiguration for improved magnetron operation.

It is a further object of my invention to provide means for removing thenon-useful electrons from a magnetron space charge chamber.

According to my invention, the anode segments defining the cylindricalspace charge chamber through which an electron-emitting cathode extendsare shaped to provide interaction gaps between adjacent segments whosecenter portions nearer the ends of the anode segments with respect tothe desired direction of rotation of the space charge around thecathode. The space charge rotation is established by conventionalorthogonally aligned static electric and magnetic fields. When the anodesegments are interconnected to provide resonant circuits between them,the alternating electric fields established across the gaps duringoperation of themagnetron have a component parallel to the axis of thespace charge chamber. This component produces a corresponding axialforce on the in-phase useful electrons which is directed inwardly fromthe ends of the anode towards the center portion, thus bunching theuseful space charge so that it traverses the leading center portions ofthe gaps. The out-of-phase electrons are subjected to oppositelydirected axial forces, thus. throwing them to the ends of the spacecharge chamber. of-phase electrons would otherwise cause cathode Due totheir high kinetic energy the out- 2 backheating if they remained in thespace charge chamber. At the same time, the useful in-phase portion ofthe space charge is retained for efficient operation.

The features of my invention which I believe to be novel are describedwith particularity in the appended claims. The invention itself,however, both as to its method of operation together with furtherobjects and advantages thereof, may best be understood by reference tothe following description taken in connection with the accompanyingdrawing in which Fig. 1 is a perspective view of a magnetron dischargedevice embodying my invention; Fig. 2 is an enlarged view of the anodesegment arrangement of Fig. 1; Fig. 3 is a sectional view of anothermagnetron embodying my invention; Fig. 4 is an end view of the anode ofFig. 3; Fig. 5 is a development of the anode segments illustrating theconfiguration of the interaction gaps of Fig. 4; and Fig. 6 is a similardevelopment illustrating a modified gap configuration.

Referring now to Fig. 1, I have shown my invention embodied in amagnetron device having a generally cylindrical evacuated glass envelopeI having its open end sealed to a metallic base or header member 2. Ananode structure 3, which may suitably take the form of a rectangularcopper block, has its base conductively secured to the header. A centralopening 4 through the thickness of the block and communicating with theupper surface of the block defines the resonant circuit. Thus conductiveside portions 5 and 6 of the anode block on diametrically opposite sidesof the opening 4 are spaced from each other at the upper portion of theblock and are connected in circuit by the base portion of the block.

The facing portions of the anode segments 5 and 6 are shaped to define acylindrical space charge chamber 1 between them commensurate in lengthwith the block thickness together with interaction gaps 8 and 9 betweenthe facing segments of portions 5 and 6 on diametrically oppo site sidesof the space charge chamber 1. An elongated cathode III, which maysuitably comprise a wire helix coated with electron-emitting alkalineearth oxides, is centrally disposed within the space charge chamber 1and coaxial therewith. The ends of the cathode extend beyond the ends ofthe-space charge chamber so that the cathode is conductively supportedbetween the ends of a pair of upright cathode support rods II which areinsulatingly sealed through the metal header 2. The cathode is entirelyconventional and is adapted to provide electrons for the magnetron spacecharge when it is suitably heated, as by applying a heating currentvoltage across the ends of the support rods ll extending through theheader. A pair of conductive cathode end shields or collector electrodes12 are respectively positioned near the opposite ends of the spacecharge chamber and are suitably supported by the cathode ends and byauxiliary support members l3 each connected between a support rod II andan adjacent end shield l2. The shields are preferably shaped as disks ofa diameter somewhat larger than that of the space charge chamber inorder that electrons expelled from the chamber may be collected thereon.

An output coupling means 14 is employed to transfer the high frequencyoutput ener y to a desired load. As shown in the drawing the outerconductor l of a concentric transmissionline coupling section isconductively secured to the header 2 and the inner conductor" lit isinsulatingly sealed through the header 2 and the base of anode block 3in order to provide an inductive pickup loop within the anode opening 4.

In accordance with myinvention, as may be seen more clearly in Fig. 2,the interaction gaps '8 and 9 between the opposing faces or segments ofthe anode portions '5 and 5 are not provided with straight gap-definingedges but instead have a chevron shape. As oriented in Figs. 1 and 2,the apex of each chevron, a viewed from the cathode, is positionedmidway along the length of the gap and is directed in a counterclockwisedirection of rotation about the cham- 9 her. Thus, it may be seen thatwith respect to a given direction of space charge rotation around thecathode, the ends of each gap lag its center portion. This direction ofspace charge rotation is provided in operation when a static magneticfield, such as may be supplied by the sole noid schematicallyrepresented by the coil il in l, is supplied through the space chargechamber 1 and coaxial therewith, and a radial electric field is suppliedbetween the cathode and the anode by applying a positive voltage to theanode block A with respect to the cathode. This space charge excites theresonant anode circuit in a conventional manner in that electrons inphase with the alternating electric field induced between the anodesegments on opposite sides of gaps 8 and 9 give up part of their kineticenergy to the field.

Referring again to Fig. 2 where the chevron configuration of the gaps 3may be more clearly viewed, it is apparent that the alternating electricfield between the facing segments of the anode portions 5 and 6 onopposite sides of the gap 8 has a substantial component parallel to thespace charge chamber axis. The relative magnitude of this axialcomponent as compared with the component in planes transverse to thespace charge chamber axis depends upon the chevron apex angle. Thus inthe construction shown in the drawing where the apex angle isapproximately l50-, the half-lengths of the gap edges on either side ofthe midpoint of the gap are at an angle of with respect to the cathodeaxis and; the axial component of the total electric field isproportional to the sine of that angle. While the magnitude of the anglemay vary, it is desirably less than in order that-a major proportion ofthe alternating electric field may b tangential to the. cathode axis forefiective ex- --citati'on of the output circuit.

' center.

Whether this axial component of the alternating electric field isdirected inwardly towards the center of the gaps or outwardly from thegap apex towards the end spaces depends upon the phase of the electronscrossing the gap. Thus, when the electrons cross the interaction gapsubstantially in phase with the electric field, that is, when theelectrons travel from a positively charged edge of the gap to thenegatively charged edge, the electrons must work against the field andgive up part of their kinetic energy to the resonant output circuit ofthe magnetron. For these in-phase or useful electrons there is anelectric field force directed inwardly from the end portions of the gaptowards the Accordingly, the useful electrons are bunched near thecenter of the space charge chamber and do not tend to stray towards theend spaces beyond the thickness of the anode block.

Conversely, out-of-phase electrons which arrive at gap 8 or 9 with avelocity component opposing the alternating' electric field across thegap are subject to an axial force directed towards the end spaces beyondthe space charge chamber where they may be easily collected by collectorelectrodes l3 and I4. Removal of these electrons is especially desirablesince they subtract energy from the resonant output system and, becauseof the increased velocity thereby gained, normally tend to return to thecathode Where they cause backheating.

Obviously, of course, an additional number of anode segments and henceadditional number of chevron-shaped gaps may be employed withoutdeparting from the spirit of my invention, so long as the centralportions of the gaps lead the end portions with respect to the desireddirection of rotation of magnetron space charge in order to provide theaxial component of the like anode block assembly it preferably made ofsuperposed upper and lower disk members [9 and It. A central opening 20in the anode assembly provides a cylindrical space charge chamber inwhich a cathode 2 i, which may suitably take the form of an electronemitting cylindrical sleeve containing a thermionic heater within, iscentrally disposed. A plurality of hole and slot cavity resonators 22are incorporated into the anode assembly which communicate throughexcitation slots within the central opening 20.

Thus, as viewed from the cathode or space charge chamber axis, a seriesof anode segments 23 are spaced from each other by interaction gaps 24.In the specific embodiment illustrated, eight cavity resonators areemployed, but of course, a greater or lesser number may be alternativelybe employed.

In accordance with my invention the edges of each anode segment 23 areshaped to define chevron-shaped interaction gaps 24. The central portionoi each gap, that is, the mid-length portion, comprises the apex of thechevron which leads the end portions of the. gap with respect to a givendirection of electron space charge. rotation around the space chargechamher 20. This configuration, which corresponds with that of theinteraction gaps in the embodiment shown in Figs. 1 and 2, is furtherillustrated in Fig. 5 which is a developed view of the anode segment 23and interaction gaps 24 as viewed from the cathode. This construction isfacilitated by the laminated anode assembly, th hole and slot resonators22 of the separate anode members It and ZEI being separately machined orotherwise formed with their radial center planes at an angle, preferablyless than 30 from a vertical center plane. As described in relation tothe embodiment of Figs. 1 and 2 an axial static magnetic field and aradial static electric field are established in the space charge chamberof the magnetron to provide the desired direction of space chargerotation. Due to the particular configuration of the gaps in which thecentral portion leads the end portions with respect to the direction ofspace charge velocity, an axial component of the induced alternatingelectric field is established. This results in bunching of the in-phaseor useful electrons near the center of the space charge member and theexpulsion of out-oi-phase or non-useful electrons into the anode endspaces. Cathode end shields 25, shown in Fig. 3 and corresponding to theend shields I2 of Fig. 1, may be suitably employed to collect theunwanted electrons.

It is not necessary that the gap configuration referred to herein aschevron-shaped be one in which the apex of the chevron is sharplydefined. For example, as shown in the development view of Fig. 6 whoselayout corresponds with that of Fig. 5, the gaps 24 between the anodesegments 23 may be more generally curved. It is important, however, thatthe curves all have their central portions leading their end portionswith respect to the space charge direction, and hence may be consideredas convex in that direction.

While I have shown and described particular embodiments of my invention,it will be obvious to those skilled in the art that changes andmodifications may be made without departing from my invention in itsbroader aspects, and I, therefore, aim in the appended claims to coverall such changes and modifications as fall within the true spirit andscope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A magnetron anode structure comprising a plurality of anode segmentsof given length defining a cylindrical space charge chamber withadjacent edges of adjacent segments defining chevron-shaped interactiongaps.

2. A magnetron anode structure comprising a plurality of anode segmentsof given length defining a cylindrical space charge chamber with thesegment edges defining chevron-shaped interaction gaps between adjacentsegments, the apex of the gaps being midway between ends of thesegments.

3. A magnetron discharge device comprising an elongatedelectron-emitting cathode extending along a given axis, a plurality ofanode segments surrounding said cathode and defining a cylindrical.space charge chamber coaxial therewith with adjacent segments spacedfrom each other, and resonant circuit means interconnecting saidsegments, said segments defining chevron-shaped interaction gaps betweenadjacent segments.

4. A magnetron discharge device comprising an elongatedelectron-emitting cathode extending along a given axis, an anodestructure comprising a plurality of spaced anode segments surroundingsaid cathode and defining a cylindrical space charge chamber coaxialtherewith, resonant circuit means interconnecting said segments, saidsegments defining chevron-shaped interaction gaps between adjacentsegments, and collector shields positioned near the ends of said spacecharge chamber.

5. A magnetron discharge device comprising an elongatedelectron-emitting cathode extending along a given axis, an anode blocksurrounding said cathode and defining a cylindrical space charge chambercoaxial therewith, said anode block incorporating a plurality of cavityresonators communicating with said space charge chamber and with theanode segments between said resonators defining a plurality ofchevronshaped interaction gaps.

6. A magnetron discharge device comprising an elongated electronemitting cathode extending along a given axis, a plurality of anodesegments surrounding said cathode and defining a cylindrical space chargchamber coaxial therewith, and resonant circuit means interconnectingsaid segments, said segments defining aligned chevron-shaped interactiongaps between adjacent segments with the apex of each chevron-shaped gapdirected in a given direction around a circumference of the space chargechamber.

ELMER D. McARTl-IUR.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,233,482 Linder Mar. 4, 1941 2,412,772 Hansell Dec. 17, 19462,477,122 Garner July 26, 1949

